Le Rouge burst onto the literary scene with La Conspiration des Milliardaires [The Billionaires' Conspiracy] (1899-1900), co-written with Gustave Guitton, in which American billionaire William Boltyn uses Thomas Edison's "Metal Men" (Karel Capek coined the term "robot" only in 1920) and the power of mediums to try to become master of the world. Le Rouge and Guitton went on to produce two more novels in the same vein, La princesse des airs [The Princess of the Skies] (1902) and Le sous-marin Jules Verne [The Submarine Jules Verne] (1903).

After they quarreled and went their separate ways, Le Rouge continued to produce solo fiction such as L'Espionne du Grand Lama (1906), which introduced a Lost World inhabited by prehistoric creatures and La Reine des Éléphants [The Queen of Elephants] (1906), which featured a society of intelligent elephants.

In 1907, Le Rouge first made the acquaintance of the Swiss poet Blaise Cendrars, who later painted an affectionately colorful portrait of him in his memoir L’homme foudroyé (1945).

Le Rouge's classic mad scientist / conspiracy saga is Le Mystérieux Docteur Cornelius (1912-13). Cornelius Kramm and his brother, Fritz, rule an international criminal empire called the Red Hand. Cornelius is a brilliant cosmetic surgeon nicknamed the “Sculptor of Human Flesh” for his ability to alter people’s likenesses. The Red Hand's growing, global, evil influence eventually causes the creation of an alliance of heroes, led by Dr. Prosper Bondonnat, billionaire William Dorgan and Lord Burydan, who band together to fight and, ultimately, defeat them.